docs: def user_defined_symbols(self):
          """Return a set of symbols that have been added to symtable after
          construction.
  
          I.e., the symbols from self.symtable that are not in
          self.no_deepcopy.
  
          Returns
          -------
          unique_symbols : set
              symbols in symtable that are not in self.no_deepcopy
  
          """
          sym_in_current = set(self.symtable.keys())
          sym_from_construction = set(self.no_deepcopy)
          unique_symbols = sym_in_current.difference(sym_from_construction)
          return unique_symbols